1. Field of the Invention
The present invention relates to the improvement of an electrostatic reproducing apparatus wherein a toner image on a toner image retaining member is transferred onto an intermediate transfer member and then is further transferred therefrom onto a transfer material and fixed thereon.
2. Description of the Prior Art
As an example of the abovementioned electrostatic reproducing apparatus, an apparatus has been known to have a toner image retaining member of the drum type and an intermediate transfer member in the shape of an endless belt in close contact with the surface of the toner image retaining member, as described in Japanese Patent Publication No. 41,679/71, Patent Laid-Open No. 78,559/74, Patent Laid-Open No. 100,582/80, etc. Such an apparatus facilitates obtaining reproduced images of high quality, by a retention method wherein a plurality of the same reproduced images are obtained by forming a latent image once on the toner image retaining member and by repeating the development and transfer thereof, to make the speed of reproduction higher. In addition, has also the advantage that transfer and fixation can be made on ordinary paper even when one-component conductive toner is used as the developing toner and thereby simplification of the developing system and improvement of the quality of image, etc. can be attained. There is a problem in such an apparatus, however, that at least two rotating rolls are required to drive the belt of the intermediate transfer member and this prevents reduction of the size and weight of the reproducing apparatus.
Meanwhile, as an electrostatic reproducing apparatus in which a reduction in size and weight is achieved, an apparatus is also known which uses an intermediate transfer member formed as a roll, as described in Japanese Patent Application No. 41,679/71, Patent Publication No. 4,848/72, Utility Model Laid-Open No. 7,945/81, etc. To enable a further reduction of size and weight of the apparatus, in particular, a heat source for fixing the toner image on the transfer material is provided inside the roll-shaped intermediate transfer member. Since the toner image on the toner image retaining member needs to be transferred surely onto the intermediate transfer member in the apparatus, the roll-shaped intermediate transfer member is further provided with its elastic material layer under a surface transfer-body layer so that the contact of the surface of the toner image retaining member with the surface of the intermediate transfer member is uniformly throughout the whole width and under uniform pressure. When the intermediate transfer member is provided with the elastic material layer in this way, warming up time from the start of heating to the readiness for transfer and fixation becomes longer even with the heat source provided inside the intermediate transfer member. So as to reduce the warming up time, it is necessary to reduce the thickness of a metal roll forming the core of the intermediate transfer member as much as possible within a range wherein no deformation thereof is caused by the pressure for transfer and, further, to make the elastic material layer of the transfer member also as thin as possible. And yet it is rather difficult to shorten the warming up time, since a transfer-body layer for improving the transference of the toner image, formed of silicone or fluoride resin 500 of .mu.m thick, is usually provided on the surface of the intermediate transfer member so as to ensure the transference of the toner image from the toner image retaining member. That is, it is extremely difficult in practice to realize an electrostatic reproducing apparatus wherein a reduction of size and weight of the apparatus is achieved, transfer and fixation of the toner image are conducted surely and stably, and curtailment of the warming up time is performed in combination with the intermediate transfer member and the toner image retaining member whose surface must not allow elastic deformation.